#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>


#define NUM 1024
#define SIZE 64
#define SEP " "
//#define Debug 

char cwd[1024];
char enval[1024];
int lastcode = 0;

char* homepath()
{
    char* home = getenv("HOME");
    if(home) return home;
    else return (char*)".";
}

const char* getUsername()
{
    const char* name = getenv("USER");
    if(name) return name;
    else return "none";
}

const char* getHostname()
{
    const char* hostname = getenv("HOSTNAME");
    if(hostname) return hostname;
    else return "none";
}

const char* getCwd()
{
    const char* cwd = getenv("PWD");
    if(cwd) return cwd;
    else return "none";
}

int getUserCommand(char* command, int num)
{
    printf("[%s@%s %s]$", getUsername(), getHostname(), getCwd());
    //scanf("%s", usercommand); //默认读到空格结束，无法读取整行
    char* r = fgets(command, num, stdin); //获取成功，返回获取的字符串的起始地址
    if(r == NULL) return -1;
    command[strlen(command)-1] = '\0'; //不会越界, 因为至少要输入一个回车\n
    return strlen(command);
}

void commandSplit(char* in, char* out[])
{
    int argc = 0;
    out[argc++] = strtok(in, SEP);
    while(out[argc++] = strtok(NULL, SEP));
#ifdef Debug
    for(int i = 0; out[i]; i++)
    {
        printf("%d:%s\n", i, out[i]);
    }
#endif
}

int execute(char* argv[])
{
    pid_t id = fork();
    if(id < 0) return -1;
    else if(0 == id)
    {
        //child exec* command
        execvp(argv[0], argv);
        exit(1);
    }
    else
    {
        //father
        int status = 0;
        pid_t rid = waitpid(id, &status, 0);
        if(rid > 0)
        {
            lastcode = WEXITSTATUS(status);
            //wait success!
        }
    }
    return 0;
}

void cd(const char* path)
{
    chdir(path);
    char tmp[1024];
    getcwd(tmp, sizeof(tmp)); //获取当前工作目录
    sprintf(cwd, "PWD=%s", tmp); //将格式化的字符串输出到cwd中
    putenv(cwd);
}

int doBuild(char *argv[])
{
    if(strcmp(argv[0], "cd") == 0)
    {
        char* path = NULL;
        if(argv[1] == NULL) path = homepath();
        else path = argv[1];
        cd(path);
        return 1;
    }
    else if(strcmp(argv[0], "export") == 0)
    {
        if(argv[1] == NULL) return 1;
        strcpy(enval, argv[1]);
        putenv(enval);
        return 1;
    }
    else if(strcmp(argv[0], "echo") == 0)
    {
        if(argv[1] == NULL) 
        {
            printf("\n");
            return 1;
        }
        if(*(argv[1]) == '$' && strlen(argv[1]) > 1) 
        {
            char* val = argv[1] + 1;
            if(strcmp(val, "?") == 0)
            {
                printf("%d\n", lastcode);
                lastcode = 0;
            }
            else
            {
                const char* enval = getenv(val);
                if(enval)
                    printf("%s\n", getenv(val));
                else 
                    printf("\n");
            }
            return 1;
        }
        else 
        {
            printf("%s\n", argv[1]);
            return 1;
        }
        return 1;
    }
    return 0;
}

int main()
{
    while(1)
    {
        char usercommand[NUM];
        //1.打印提示符&&获取用户命令字符串
        int n = getUserCommand(usercommand, sizeof(usercommand));
        if(n <= 0) continue; //空串就不要往后执行了
        //2.分割字符串
        char* argv[SIZE];
        commandSplit(usercommand, argv);
        //3.检查并执行内建命令
        n = doBuild(argv);
        if(n) continue;
        //4.执行对应的字符串
        execute(argv);
    } 
    return 0;
}

